1. Field of the Invention
The invention relates to novel polymers containing amide linkages and to a process for preparing such polymers. More specifically this invention relates to polyamides containing nylon-3 units and having a high glass transition temperature. These polyamides are prepared by condensation polymerization from N,N-terephthaloyldi-beta-alanine and a diamine.
2. Description of the Prior Art
Nylon is a generic term for synthetic polyamides. The present invention pertains to nylon-3/X polymers, which contain a nylon-3 unit. This form of shorthand is used to identify the number of carbon atoms in the respective monomers which make up the polyamide. Nylon-3 is a polyamide comprised of 3 carbon units. Nylon-3/X is a copolyamide which contains groups of 3 carbon units along with any nylon fragment of the general formula: ##STR1## where R', R" and R"' are any aliphatic, alicyclic, or aromatic carbon group.
There are several known methods for producing nylon-3 type polymers using starting materials different from those of the present invention. Most polyamides are produced by a condensation polymerization process. In other words, the polymerization occurs primarily by the reaction between pairs of functional groups, with water split out. For example, the thermal condensation of beta-alanine proceeds as follows: ##STR2## where n is the number of monomer units reacted.
Nylon-3 polymers are also prepared by hydrogen transfer polymerization of acrylamide in the presence of a basic catalyst (U.S. Pat. No. 2,749,331), by processes employing beta-lactam and a ring-opening polymerization (U.S. Pat. No. 3,220,983), by condensation hydrolysis of beta aminopropionitrile (U.S. Pat. No. 3,499,874), by condensation hydrolysis of oxydipropionitrile (Japan No. 68 27,617), and by the thermal polymerization of ethylene cyanohydrin (U.S. Pat. No. 3,125,353).
Numerous combinations of diacids, diamines and amino acids have been interacted by the above methods and copolymers containing various proportions of two or more diacids, diamines or amino acids have been prepared.
The present invention pertains to nylon-3/X copolymers. These copolymers are formed by the polymerization processes described above from a monomer containing nylon-3 units combining with other suitable monomers. Most nylon-3/X copolymers are random systems which exhibit a melting point depression with increasing comonomer, i.e. X, concentration up to approximately 50 mole %. These random systems also exhibit decreased crystallinity and increased water absorption.
A typical nylon-3/X copolymer has a low glass transition temperature (Tg) of less than 70.degree. C. The glass transition temperature is the temperature at which an amorphous material changes from a brittle, vitreous state to a plastic state. A polymer or copolymer with a high Tg is suitable for high temperature structural applications. Consequently most nylon-3/X copolymers which have been produced are unsuitable for high temperature structural use.